1. Field of the Invention
The present invention relates to a mechanical push button lock for controlling a locked/unlocked state of a specific element of a machine, and more particularly to a mechanical push button lock that not only provides two stage tactile impression but also has simple structure and low manufacturing tolerance.
2. Description of the Prior Art
A mechanical push button lock is used to control the locked/unlocked state of a specific element of a machine and is in widespread use in conventional industry and many products. Possible applications include mechanical push button lock for the cover of a crystal display projector, the mechanical push button lock of door, and so on.
The conventional structure of the mechanical push button lock comprises two categories. One category provides two stage tactile impression and the other category provides a simple structure and low tolerance.
First category, as FIG. 1 shows, comprises push key 10, first cross rod 11, second cross rod 12, shaft 13, first spring 14 and second spring 15. Push key 10 located in one end of first cross rod 11, and one end of first spring 14 is located on first cross rod 11. Another end of first spring 14 is located on a fixed specific object 165 to settle first cross rod 11 in a specific region. Beside, the direction of first cross rod 11 points to second cross rod 12. Moreover, second cross rod 12 rotates around shaft 13 and second spring 15 is used to settle second cross rod 12 in another specific region by connecting second cross rod 12 with fixed specific object 16. Obviously, fixed specific object 16 and fixed specific object 165 can be the same object or be different objects, it depends on the design of mechanical push button lock. In addition, when the mechanical push button lock is locked then specific element17 also is restricted by second cross rod 12 and is locked.
Therefore, it is obvious that when push key 10 is pressed first cross rod 11 slight slides along the pressed direction and first spring 14 is transfigured. Afterwards, when first cross rod 11 touches second cross rod 12 then not only does first cross rod 11 slide along the pressed direction but also second cross rod 12 rotates around shaft 13. In other words, not only first spring 14 is transfigured but also second spring 15 is elongated. Then when second cross rod 12 rotates enough degrees, second cross rod 12 does not restrict specific element17 and then specific element 17 is unlocked.
Consequently, this category provides two stage tactile impression that is obvious to a user because the required pushed force is small before the first cross rod 11 contacts second cross rod 12 and is large after the first cross rod 11 contacts second cross rod 12.
The second category, as FIG. 2 shows, comprises push key 20, spring 21, shaft 22 and skeleton structure 23. Push key 20 is located in one end of skeleton structure 23 and specific element 24 contacts another end of skeleton structure 23 when specific element 24 is locked by the mechanical push button lock, and shaft 22 penetrates through skeleton structure 23. Moreover, spring 21 is used to settle skeleton structure 23 in a specific region by connecting skeleton structure 23 with fixed object 25.
Obviously, when push key 20 is pressed then skeleton structure 23 rotates around shaft 23, and when skeleton structure 23 rotates enough degrees then specific element 24 is relaxed and unlocked. Moreover, because only one spring 21 is transfigured, it provide a one stage tactile impression for user.
Comparing FIG. 1 and FIG. 2, it is crystal-clear that the structure of the first category is complicated and thus the cost of the first category is higher. In comparison, the structure of the second category is simplified and the cost of the second category is lower. Beside, the manufacturing process of the first category is more complicated for there are six component parts that need to be installed, but manufacturing tolerance is more sensitive in the second category because no spring is located between the push key and the shaft to absorb some manufacturing tolerance.
According to the previous discussion, it is obvious that both the conventional structures of the mechanical push button lock are required to improve, and it is therefore desired to develop a push button lock that provides two stage tactile impression, a simple structure and low manufacturing tolerances simultaneously.